Electric arc furnaces are often used in the melting of scrap and refining of steel where an electric current is used as a source of heat. Such furnaces are generally vessels that are equipped with a rotatable roof, which has electrodes associated therewith, and are carried by a tiltable base so that upon completion of refining, metal is poured from a tap hole at the lower portion of the vessel.
During operation of an electric furnace, there is a substantial problem associated with the noise pollution that is created. In addition, there are usually three steps which result in the production of large quantities of particulate matter and smoke which, with current environmental controls, cannot be discharged into the atmosphere. One of these steps is the charging of the furnace, during which the furnace roof assembly and electrodes are pivotally moved to one side of the furnace while scrap metal and/or molten metal are added to the furnace vessel such as by cable-carried scrap buckets or ladles. A second step which causes extensive pollution problems is the meltdown and refining step wherein fumes escape through various openings in the furnace during melting, during the addition of flux materials or alloying materials, and also during temperature determination and sampling. During such meltdown, noise caused by arcing has been recorded in the 120 dB range when using a 30 MVA Transformer in connection with a 60-ton furnace, and the current trend is to use ultrahigh power transformers which will substantially increase this noise problem. Very little has been done to reduce noise levels in the shop, but rather workers have merely been provided with gear to protect their ears. Following the refining step, the tapping step produces gaseous pollutants resulting from the tapping of the furnace, where the molten metal is poured into means for collecting the metal for transfer to a subsequent station, and where generally alloying ingredients are added to the molten metal.
Previous attempts to collect fumes and smoke from an electric arc furnace operation have generally focused on three systems. One system, furnace evacuation, uses an opening in the furnace roof and additional shrouds over the tap hole, electrode holes, and charging door to pick up furnace fumes. Such a system would not meet present-day codes and does not collect fumes when the roof is off the furnace for scrap charging or the fumes generated in the steel ladle while tapping. A second system provides for a canopy in the roof of the building. Because it must be placed distant from the point of fume generation, a large amount of air is admixed with the furnace fumes requiring a large and expensive gas cleaning system for cleaning the gas. In general, this system has not been successful in cleaning the shop gases because, to reduce cost, they are usually too small. Also, rising fume is subject to shop crosswinds which blow the fume away from the canopy. Also, this system allows a dirty atmosphere within the shop itself which is hazardous to the workers. A third system is complete shop evacuation which can be made to adequately collect fumes and clean gas. However, since the entire shop is evacuated, the system is very large and expensive because of the tremendous volume of gases that must be handled to adequately clean the fumes. Again, the shop atmosphere is dirty and hazardous to the workers.
In U.S. Pat. Nos. 3,724,827 and 3,743,264, which relate to Q-BOP or BOF type installations, furnace reactions are affected by oxygen or other fuel being blown into the furnace while the furnace is upright, then creating a large volume of contaminated gas that is directed into a hood affixed to the furnace mouth or slightly spaced therefrom depending on the process step carried out at a particular time. The furnace is then rotated for charging or tapping. Such systems are not, however, adaptable to electric arc furnace installations.
An object of the present invention is to provide a means for abatement of the noise associated with electric arc furnace operations.
A further object of the present invention is to provide an electric furnace station pollution control system which eliminates the need for snorkels and hoods by providing a housing to enclose the furnace and simplifying the gas collection system to make possible the use of smaller gas cleaning systems and fans.